Methods and systems for detecting a position-based attribute of an object using digital codes

PRIORITY DATA

0001This is a continuation of U.S. application Ser. No. 14/024,302 filed Sep. 11, 2013, which is a continuation of U.S. application Ser. No. 13/679,355 filed Nov. 16, 2012, which is a continuation of U.S. application Ser. No. 12/962,096, filed Dec. 7, 2010, which is a continuation of U.S. Pat. No. 7,868,874, issued Jan. 11, 2011, both of which are incorporated herein by reference.

FIELD OF THE INVENTION

0002The present invention generally relates to position or proximity sensors such as touchpads, and more particularly relates to devices, systems and methods capable of detecting a position-based attribute of a finger, stylus or other object using digital codes.

BACKGROUND

0003Position sensors are commonly used as input devices for computers, personal digital assistants (PDAs), media players, video game players, consumer electronics, wireless phones, payphones, point-of-sale terminals, automatic teller machines, kiosks and the like. One common type of sensor used in such applications is the touchpad sensor, which can be readily found, for example, as an input device on many notebook-type computers. A user generally operates the sensor by moving a finger, stylus or other stimulus near a sensing region of the sensor. The stimulus creates a capacitive, inductive or other electrical effect upon a carrier signal applied to the sensing region that can be detected and correlated to the position or proximity of the stimulus with respect to the sensing region. This positional information can in turn be used to move a cursor or other indicator on a display screen, scroll through text elements on the screen, or for any other user interface purpose. One example of a touchpad-type position sensor that is based on capacitive sensing technologies is described in U.S. Pat. No. 5,880,411, which issued to Gillespie et al. on Mar. 9, 1999.

0004While touchpad-type sensors have been in use for several years, engineers continue to seek design alternatives that reduce costs and/or improve sensor performance. In particular, significant attention has been paid in recent years to reducing the effects of noise generated by display screens, power sources, radio frequency interference and/or other sources outside of the sensor. Numerous sampling, filtering, signal processing, shielding, and other noise-reduction techniques have been implemented with varying levels of success.

0005Accordingly, it is desirable to provide systems and methods for quickly, effectively and efficiently detecting a position-based attribute of an object in the presence of noise. Other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

0006Methods, systems and devices are described for detecting a position-based attribute of a finger, stylus or other object with a touchpad or other sensor. According to various embodiments, the sensor includes a touch-sensitive region made up of any number of electrodes arranged in an appropriate fashion to detect user input. Modulation signals for one or more electrodes are produced as a function of any number of distinct discrete digital codes, which may be substantially orthogonal to each other. The modulation signals are applied to an associated at least one of the plurality of electrodes to obtain a resultant signal that is electrically affected by the position of the object. The resultant signal is demodulated using the plurality of distinct digital codes to discriminate electrical effects produced by the object. The position-based attribute of the object is then determined with respect to the plurality of electrodes from the electrical effects.

BRIEF DESCRIPTION OF THE DRAWINGS

0007Various aspects of the present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and

0008<figref idref="DRAWINGS">FIGS. 1A-B</figref> are block diagrams showing exemplary sensing devices;

0009<figref idref="DRAWINGS">FIG. 2</figref> is a flowchart showing an exemplary process for detecting a position-based attribute of an object;

0010<figref idref="DRAWINGS">FIG. 3A</figref> is a is a frequency domain plot for an exemplary received signal;

0011<figref idref="DRAWINGS">FIG. 3B</figref> is a frequency domain plot for an exemplary demodulated signal;

0012<figref idref="DRAWINGS">FIG. 4</figref> is a depiction of an exemplary scenario for processing electrical images of sensed objects;

0013<figref idref="DRAWINGS">FIG. 5</figref> is a block diagram of an exemplary sensing device capable of sensing multiple position-based attributes in two dimensions;

0014<figref idref="DRAWINGS">FIGS. 6A and 6B</figref> are block diagrams of exemplary sensing devices with a filtering capacitor: one with simultaneous sensing of multiple signal channels on a common receive electrode, and the other with unified modulation and receive electrodes;

0015<figref idref="DRAWINGS">FIG. 7</figref> is a block diagram of an exemplary sensing device formed on a single substrate; and

0016<figref idref="DRAWINGS">FIG. 8</figref> is a block diagram of an exemplary sensing device formed on a flexible substrate.

DETAILED DESCRIPTION

0017The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

0018According to various exemplary embodiments, spread spectrum techniques can be applied within a position sensor such as a touchpad to improve noise immunity and/or to provide performance enhancements. Code division multiplexing (CDM), for example, can be used to create two or more distinct modulation signals that are applied to sensing electrode(s) within the sensor, thereby increasing the effective power of the applied signals. Coded spread spectrum modulation may refer to direct sequence, frequency hopping, time hopping or various hybrids of these or other techniques. Because the modulation frequencies applied to the sensitive region cover a wider spectrum than was previously received, narrow band noise occurring at a particular frequency or moderate wide band noise, uncorrelated with the coded modulation, has a minimal effect upon the narrower overall demodulated signal channels. The effect of noise on multiple signal channels may also be more uniform so that a minimum signal-to-noise ratio (SNR) is maintained for each useful signal channel. This concept can be exploited even further by selecting digital codes to produce frequency-domain signals that avoid known sources of noise. Spread spectrum techniques can therefore apply increased power to the sensing region while reducing the effects of noise, thereby resulting in a significantly improved SNR for the sensor in comparison to conventional time-domain multiplexing techniques of a comparable sample period. Spread spectrum techniques applied within the sensor may enable other beneficial sensor designs and features as well. These concepts are explored more fully below.

0019As used herein, the term “position sensor” is intended to encompass not only conventional touchpad devices, but also a broad range of equivalent devices that are capable of detecting the position or proximity of one or more fingers, pointers, styli or other objects. Such devices may include, without limitation, touch screens, touch pads, touch tablets, biometric authentication devices (e.g. fingerprint sensors), handwriting or character recognition devices, and the like. Similarly, the terms “position”, “object position” and “position-based attribute” as used herein are intended to broadly encompass various types of absolute or relative positional or proximity information, and also other types of spatial-domain information such as speed, velocity, acceleration, and the like, including measurement of motion in one or more directions. Various position-based attributes may also include time history components, as in the case of gesture recognition and the like. Accordingly, many different types of “position sensors” may be capable of detecting widely varying “position-based attributes” beyond the mere presence or absence of an object in a wide array of alternate but equivalent embodiments determined by their applications.

0020Turning now to the drawing figures and with initial reference to <figref idref="DRAWINGS">FIG. 1A</figref>, an exemplary sensor <b>100</b> suitably includes a sensing region <b>101</b>, a controller <b>102</b>, a modulator <b>107</b>, with associated drive circuitry <b>109</b>, and a demodulator <b>117</b> with associated receiver circuitry <b>115</b> as appropriate. A position-based attribute of a finger, stylus or other object <b>121</b> is detected by applying various modulation signals <b>110</b>A-D to electrodes <b>112</b>A-D that, along with sensing electrode <b>114</b>, define sensing region <b>101</b>. The modulation signals <b>110</b>A-D are capacitively or otherwise electrically coupled to one or more receiving electrodes <b>114</b>, thereby forming any number of data transmission channels <b>113</b>A-D. Electrical effects produced by object <b>121</b> upon channels <b>113</b>A-D can be subsequently identified in signals <b>116</b> received by the receive electrode, and these received signals can be subsequently processed to isolate the location of object <b>121</b> with respect to electrodes <b>112</b>A-D within sensing region <b>101</b>. An example of a conventional technique for capacitively sensing and processing object position in a touchpad is set forth in U.S. Pat. No. 5,880,411, referenced above, although any other sensing techniques could be used in a wide array of alternate embodiments.

0021Although various types of sensors <b>100</b> are capable of detecting different electrical effects produced by object <b>121</b>, the exemplary embodiments of <figref idref="DRAWINGS">FIGS. 1A-B</figref> show configurations for monitoring changes in capacitance across sensing region <b>101</b> caused by the presence or absence of object <b>121</b>. More particularly, as modulation signals <b>110</b>A-D are applied to electrodes <b>112</b>A-D, a “virtual capacitor” is formed between each electrode <b>112</b>A-D transmitting the modulated signal and a receiving electrode <b>114</b>. If an object is present within the fields created by this capacitor, the capacitance between the transmitting electrode <b>112</b> and the receiving electrode <b>114</b> is affected. Typically, the effective capacitance between electrodes <b>112</b> and <b>114</b> is reduced if a grounded (or virtually grounded) object such as a finger is present, and the effective capacitance is increased if an ungrounded conductor (e.g. a stylus) or higher dielectric object is present. In either case, the change in capacitance caused by the presence of object <b>121</b> is reflected in the output signal <b>116</b> such as voltage, current, or charge measured from receive electrode <b>114</b>.

0022By monitoring signals <b>116</b> produced by each modulation signal <b>110</b>A-D, then, the presence of object <b>121</b> with respect to each electrode <b>112</b>A-D (respectively) can be determined. In the exemplary embodiment shown in <figref idref="DRAWINGS">FIG. 1A</figref>, four sensing channels <b>113</b>A-D are shown arranged in a one-dimensional sensing array <b>101</b>. In the exemplary embodiment of <figref idref="DRAWINGS">FIG. 1B</figref>, seven channels <b>113</b>A-G are implied with several channels <b>113</b>A-C arranged in a first direction between <b>112</b>A-C and <b>114</b>, and the remaining channels <b>113</b>D-G arranged in a substantially orthogonal direction between <b>112</b>D-G and <b>114</b> to allow for detection of image “silhouettes” in two dimensions, as described more fully below with reference to <figref idref="DRAWINGS">FIG. 4</figref>. In practice, as few as one channel (e.g. a button) or as many as dozens, hundreds or even more sensing channels could be arranged in any single or multi-dimensional pattern in a wide array of alternate embodiments. Properly arranged, the position of an object <b>121</b> with respect to sensing region <b>101</b> can be determined from the electrical effects produced by object <b>121</b> upon the transmission of modulation signals <b>110</b>A-D applied to the various electrodes. These effects, in turn, are reflected in the received signals <b>116</b> that are demodulated and subsequently processed as appropriate to arrive at output signal <b>120</b>.

0023Further, sensor <b>100</b> may be readily configured or re-configured to create any type or number of sensing zones within region <b>101</b> by simply assigning or re-assigning digital codes used to create modulation signals <b>110</b>. As shown in <figref idref="DRAWINGS">FIGS. 1A-B</figref>, each receiving electrode <b>114</b> may receive signals coupled by any number of signal channels <b>113</b>, thereby resulting in multiple result signals <b>116</b> being provided on a single path. Because signals <b>116</b> are provided on a common path, sensing channels <b>113</b> of any number of electrodes may be created on a permanent or temporary basis by simply applying a common modulation signal <b>110</b> (e.g. a modulation signal <b>110</b> formed from a common digital code) to each of the transmit electrodes <b>112</b> making up the sensing zone. Sensing zones within region <b>101</b> may overlap and/or vary with time, and are readily re-configurable through simple application of different digital codes to one or more electrodes <b>112</b>. More than one electrode may be part of a channel, and more than one channel modulation may be applied to an electrode.

0024In a traditional sensor, modulation signals <b>110</b>A-D are typically simple sinusoidal or other periodic alternating current (AC) signals applied sequentially to the various channels using any form of time domain multiplexing (TDM). By applying spread spectrum concepts commonly associated with radio communications to sensor <b>100</b>, however, numerous benefits can be realized. In particular, digital coding techniques similar to those used in code division multiple access (CDMA) radio communications can be employed to create distinct modulation signals <b>110</b>A-D that can be simultaneously applied to the various sensing zones of region <b>101</b>, thereby potentially reducing the switching complexity of sensor <b>100</b>.

0025Spread spectrum techniques applied within sensor <b>100</b> may provide additional benefits, such as improved resistance to noise. Because each signal channel <b>113</b> results from the application of an appropriate digital code, for example, principles of code gain can be readily exploited to improve the performance of sensor <b>100</b>. The gain of each modulation signal <b>110</b> applied to one or more transmit electrodes <b>112</b> increases with the length of the code. Through the use of conventional code generation techniques, combinatorial variations of the digital codes with well-known spectral and correlation properties are relatively easy to generate. Further, these combinatorial variations provide a relatively large pool of potential distinct digital codes from which to create modulation signals <b>110</b> with desirable time or frequency domain characteristics, as described below. Additional detail about particular code generation and signal processing techniques are described more fully below.

0026Again with reference to <figref idref="DRAWINGS">FIGS. 1A-B</figref>, sensing region <b>101</b> is any capacitive, resistive, inductive or other type of sensor that is capable of detecting the position, proximity and/or other position-based attribute of a finger, stylus or other object <b>121</b>. Exemplary sensing regions <b>101</b> include the various sensors produced by Synaptics Inc. of Santa Clara, Calif., which appropriately detect a one dimensional, two dimensional or multi-dimensional position of an object <b>121</b> using capacitive or inductive coupling, although many other sensing regions <b>101</b> could be used in a wide array of alternate embodiments. Other types of sensing regions <b>101</b> capable of detecting position or proximity include sensors based upon acoustic, optical, or electromagnetic properties (e.g. radio frequency, infrared, ultraviolet or the like), and/or any other effects.

0027Controller <b>102</b> is any processor, microcontroller, neural network, analog computer, programmed circuitry, or other module capable of processing input data <b>118</b> to extract output indicia <b>120</b> and/or the like. The particular control circuitry <b>102</b> used varies widely from embodiment to embodiment, but in exemplary embodiments controller <b>102</b> is a model T1004, T1005, T10XX or other microcontroller produced by Synaptics Inc. of Santa Clara, Calif. In many embodiments, controller <b>102</b> includes and/or communicates with a digital memory <b>103</b> that suitably stores digital instructions in any software or firmware form that are executable by controller <b>102</b> to implement the various sensing, control and other functions described herein. Alternatively, the functions of memory <b>103</b> may be incorporated into controller <b>102</b> such that a physically distinct memory device <b>103</b> may not be present in all embodiments. The physical controller may also incorporate more elements including the drive circuitry <b>109</b> and receive circuitry <b>115</b>, as well as, others described.

0028Code generation module <b>104</b> is any discrete or integrated circuit, device, module, programming logic and/or the like capable of producing digital codes <b>106</b> that can be used in generating modulation signals <b>110</b>A-D. The number, size and types of digital codes produced vary significantly, but in various embodiments the codes are substantially orthogonal to each other, and are of sufficient length to provide for enough distinct digital codes to be associated with each sensing zone of region <b>101</b>. The discrete codes may be binary, ternary, or generically multi-level, and may indicate both driven and un-driven states (tri-state). Various circuits, modules and techniques for generating digital codes suitable for use with CDM include shift register sequences such as Walsh-Hadamard codes, m-sequences, Gold codes, Kasami codes, Barker codes, delay line multiple tap sequences, and/or the like. Alternatively, digital codes may be pre-determined and stored in a lookup table or other data structure within controller <b>102</b> and/or memory <b>103</b>, and/or may be generated by controller <b>102</b> using any suitable algorithm. In such embodiments, code generation module <b>104</b> may not be present as a separate physical element from controller <b>102</b>, but rather should be considered to be a logical module representing the code generation and/or retrieval function carried out by controller <b>102</b> or other digital processing devices as appropriate.

0029The term “substantially orthogonal” in the context of the distinct digital codes is intended to convey that the distinct codes need not be perfectly orthogonal from each other in the mathematical sense, so long as the distinct codes are able to produce meaningful independent results. Strict orthogonality may thus be traded off for various other properties such as correlation, spectra, or compressibility. Similarly, the term “sensing zone” is intended to convey that a single code could be applied to multiple electrodes <b>112</b> to create a single zone of sensitivity that encompasses a larger portion of sensing region <b>101</b> than any of the individual electrodes <b>112</b>. Also, more than one code could be applied to an electrode creating overlapping or spatially filtered “sensing zones”. For example phase delayed or “shifted” versions of the same code sequence can be distinct and substantially orthogonal such that they are readily distinguishable. In various cases, interpolation between phase shifts may even be possible.

0030Modulator <b>107</b> is any circuit, logic or other module capable of producing modulation signals <b>110</b>A-D using the distinct digital codes produced by module <b>104</b>. Typically, modulator <b>107</b> modulates a carrier signal <b>111</b> with the digital codes <b>106</b> using any type of amplitude modulation (AM), frequency modulation (FM), phase modulation (PM) or another suitable technique to create modulation signals <b>110</b>A-D. Accordingly, modulator <b>107</b> may be implemented using any conventional digital and/or analog circuitry, or may be partially or entirely implemented with software logic executing within controller <b>102</b> or the like. Carrier signal <b>111</b> may be produced by any oscillator or other signal generator <b>105</b> as appropriate. In one embodiment suitable for use in a capacitively-sensing touchpad, signal <b>111</b> can be produced at frequencies that range from about 10 kHz-100 MHz, although these signals may be produced at any frequency or range in a wide array of equivalent embodiments. Additional detail about an exemplary modulation function is described below with respect to <figref idref="DRAWINGS">FIG. 3</figref>. In still other embodiments, carrier signal <b>111</b> is eliminated and spectral components of the applied modulation signals <b>110</b>A-D are determined from the clock rate, repeat lengths and/or other aspects of the digital codes. The carrier signal <b>111</b> may therefore be eliminated and/or conceptualized as a direct current (DC) signal in various alternate embodiments.

0031Modulation signals <b>110</b>A-D are applied to electrodes <b>112</b>A-D of sensing region <b>101</b> in any manner. In various embodiments, modulator <b>107</b> suitably applies the signals to the appropriate electrodes <b>112</b>A-D via any drive circuitry <b>109</b>, which includes any sort of scaling amplifier, multiplexer, switch to any current or voltage source, charge transfer device, controlled impedance, and/or the like. <figref idref="DRAWINGS">FIG. 1A</figref> shows a plurality of signal paths <b>109</b>A-<b>109</b>D coupling the modulator <b>107</b> to corresponding transmitter electrodes <b>112</b>A-<b>112</b>D. Alternatively, a single driver circuit <b>109</b> may be used to interconnect modulator <b>107</b> and sensing region <b>101</b> in a serial fashion, although in practice drive circuitry <b>109</b> will typically include multiple amplifiers, multiple drivers and/or other signal paths providing parallel connections between modulator <b>107</b> and the various electrodes <b>112</b> within sensing region <b>101</b> to permit multiple sensing channels <b>113</b> to be driven by modulated electrodes <b>112</b> simultaneously with the same or different signals.

0032As noted above, modulation signals <b>110</b>A-D are provided to electrodes <b>112</b>A-D in sensing region <b>101</b>, and resultant signals <b>116</b> from receiving electrode <b>114</b> are provided to a suitable demodulator <b>117</b>. A scaling amplifier, multiplexer, filter, discriminator, comparator, and/or other receiving circuitry <b>115</b> may be provided as well to shape received signals <b>116</b>. Demodulator <b>117</b> is any circuit or other module capable of demodulating the output <b>116</b> of sensing region <b>101</b> to identify any electrical effects produced by object <b>121</b>. Demodulator <b>117</b> may also include and/or communicate with a demodulation filter, such as any suitable digital or analog low-pass or band-pass filter, as well as any conventional analog-to-digital converter (ADC). In various embodiments, demodulator <b>117</b> receives carrier signal <b>111</b> and/or the phase shifted versions of the distinct digital codes <b>106</b> to allow demodulation of both signals. Alternatively, demodulator <b>117</b> provides analog demodulation of carrier signal <b>111</b> and provides the resultant signals to controller <b>102</b> and/or receiving circuitry <b>115</b> for subsequent processing. Similarly, the demodulation function represented by module <b>117</b> in <figref idref="DRAWINGS">FIG. 1</figref> may be logically provided in hardware, software, firmware and/or the like within controller <b>102</b> and/or another component, thereby removing the need for a separately-identifiable demodulation circuit <b>117</b>.

0033During the operation of sensor <b>100</b>, any number of distinct digital codes are produced by code generation module <b>104</b> and modulated with a carrier frequency to create a set of modulation signals <b>110</b>A-D applied to any number of electrodes <b>112</b>A-D within sensing region <b>101</b>. The position of object <b>121</b> with respect to sensing region <b>101</b> electrically affects one or more output signals <b>116</b> provided from sensing region <b>101</b>. By demodulating the resultant signals <b>116</b>, the electrical effects can be identified and subsequently processed by controller <b>102</b> or the like to determine a position-based attribute relating to object <b>121</b>. By modulating the electrodes with an appropriate digital code, the narrower sensing frequency for the sensor is effectively spread across multiple frequencies, thereby improving noise rejection. Moreover, the use of code division multiplexing allows each of the modulation signals <b>110</b>A-D to be applied simultaneously, thereby reducing or eliminating the need for separate time domain switching and control in many embodiments. The electrical effects identified from sensing region <b>101</b> using spread spectrum techniques may be further processed by controller <b>102</b> and/or another processing device as appropriate.

0034With reference now to <figref idref="DRAWINGS">FIG. 2</figref>, an exemplary process <b>200</b> for detecting a position-based attribute of an object with respect to a sensing region <b>101</b> suitably includes the broad steps of producing a set of distinct digital codes for modulation signals <b>110</b>A-D (step <b>201</b>), demodulating each of the response signals <b>116</b> that result from the application of modulation signals <b>110</b>A-D (steps <b>204</b>, <b>206</b>), and determining one or more position-based attributes of object <b>121</b> from the electrical effects identified within the response signals <b>116</b> (step <b>208</b>). In various further embodiments, the particular digital codes generated in step <b>201</b> may be modified (step <b>210</b>) to reduce the effects of noise, reducing interference on other devices caused by this device, or for any other purpose. Additional processing may also be performed (step <b>212</b>), such as single or multi-object processing, rejection of undesired image data, and/or the like.

0035Although the flowchart shown in <figref idref="DRAWINGS">FIG. 2</figref> is intended to show the various logical steps included in an exemplary process <b>200</b> rather than a literal software implementation, some or all of the steps in process <b>200</b> may be stored in memory <b>103</b> and executed by controller <b>102</b> alone and/or in conjunction with other components of sensor <b>100</b> (e.g. code generation module <b>104</b>, modulator <b>107</b>, demodulator <b>117</b> and/or the like). The various steps may be alternately stored within any digital storage medium, including any digital memory, transportable media (e.g. compact disk, floppy disk, portable memory and/or the like), magnetic or optical media, and/or the like. The various steps of process <b>200</b> may be applied in any temporal order, or may be otherwise altered in any manner across a wide array of alternate embodiments. Further, the various steps shown in <figref idref="DRAWINGS">FIG. 2</figref> could be combined or otherwise differently organized in any manner.

0036As noted above, the distinct digital codes <b>106</b> used to create modulation signals <b>110</b>A-D may be produced in any manner (step <b>201</b>), such as by any type of hardware or software logic represented by code generation module <b>104</b> in <figref idref="DRAWINGS">FIG. 1</figref>. Any number of feedback shift registers, for example, can be configured in a maximum length sequence (MLS) or the like to generate a pseudo-random digital code of any desired length that could be readily applied in a variety of phases and/or sums as distinct code sequences to the various modulation signals <b>110</b>A-D. The resulting sequence of binary codes <b>106</b> emanating from parallel shift registers is generally spectrally flat, with the exception of a minimal DC term. In an alternate embodiment, a MLS or other routine for generating digital codes <b>106</b> may be simulated in software executing within controller <b>102</b>, or elsewhere as appropriate. In still other embodiments, codes <b>106</b> are generated prior to use and stored in a lookup table or other data structure in memory <b>103</b>, or the like. In various alternate but equivalent embodiments, controller <b>102</b> may directly generate or retrieve codes <b>106</b> and/or may produce them by directing the operation of a separate code generation module <b>104</b> or the like. As noted above, the particular codes may be generated in any manner. A digital bit sequence may be simply shifted in phase, for example, to create multiple distinct codes. Alternatively, distinct codes can be computed from other codes using a variety of methods including summation, exclusive-or, and multiplication, and/or other techniques of generating high dimensionality random and pseudo-random sequences. Code generation techniques based upon exclusive-or or multiplication operations may provide an additional benefit of generating linear combinations that may be useful in some embodiments.

0037The various codes <b>106</b> are then used to modulate or otherwise create the particular modulation signals <b>110</b>A-D that are applied to the various sensing electrodes <b>112</b>A-D in sensing region <b>101</b> (step <b>202</b>). As described above, the applied signals are electrically affected by the presence of object <b>121</b>, with the resultant electrical effects being determinable from received signal <b>116</b> (step <b>203</b>).

0038Demodulating received signal channels <b>113</b> (in step <b>204</b>) suitably involves extracting information about the position of object <b>121</b> from the modulated signals. Such extraction typically involves reversing the modulation process described above. Accordingly, demodulator <b>117</b> typically receives carrier signal <b>111</b> (or another signal that is synchronous with signal <b>111</b>) for performing analog demodulation and/or signal discrimination (e.g. distinguishing between noise and desired signal) in addition to the particular digital code <b>106</b> that previously modulated the carrier signal used to create the particular resultant signal <b>116</b>. Because the sensor both transmits and receives, it is rarely necessary to recover the carrier or code sequence.

0039Demodulation may be carried out for any number of received signal channels <b>113</b>, as appropriate (step <b>206</b>). In the exemplary sensor <b>100</b> shown in <figref idref="DRAWINGS">FIG. 1A</figref>, signal <b>116</b> resulting from the transmission of each signal channel from the modulated electrodes <b>112</b>A-D are received on a common path emanating from receiving electrode <b>114</b>. Even if the various sensing channels <b>113</b>A-D are all active at the same time (e.g. modulation signals <b>110</b>A-D are simultaneously provided to each modulated electrode <b>112</b>A-D), however, the resulting signals <b>116</b> produced by each channel <b>113</b>A-D can be demodulated using conventional CDM demodulation techniques. Particular components (or channels) of resultant signal <b>116</b> produced in response to any modulation signal <b>110</b>A-D can therefore be readily extracted. This concept can be exploited in myriad ways, as described below, to create a number of additional features and performance enhancements within sensor <b>100</b>. A common modulation signal <b>110</b>A-D, for example, could be applied to multiple electrodes <b>112</b>A-D to increase the size of any particular sensing zone within region <b>101</b>. These zones can be readily adjusted during operation to create various operating modes or the like. To make the entire sensing region <b>101</b> act as a single button, for example, each electrode <b>112</b>A-D could be provided with the same modulation signal <b>110</b> without otherwise adjusting the performance of the sensor. Because all of the signals resulting from receive electrode <b>116</b> are provided on a common path in <figref idref="DRAWINGS">FIG. 1</figref>, simply demodulating the entire received signal using the common modulation code will identify the presence of object <b>121</b> anywhere within sensing region <b>101</b> in this case. Similar concepts can be applied to create any number of independent or overlapping sensing zones across sensing region <b>101</b> through simple manipulation of digital code sequences <b>106</b>. Furthermore, spatial frequency filtering can be done simply through proper modulation and demodulation, for example to accomplish palm rejection or to reject other inappropriate inputs.

0040The demodulated signals <b>118</b> are appropriately received at controller <b>102</b> so that the position-based attribute of object <b>121</b> can be determined (step <b>208</b>). These signals may be filtered digitally or as analog, using linear and non-linear filters. Various techniques for identifying the position of object <b>121</b> with respect to the various electrodes <b>112</b>A-D include detection of peak electrical effect, computation of a centroid based upon the electrical effects, comparison of differences in electrical effects observed between electrodes <b>112</b>A-D, comparison of changes in electrical effects over time, interpolation between signal channels from the electrodes, and/or according to many other techniques. In the case of peak detection, the position of object <b>121</b> is associated with one or more electrodes <b>112</b>A-D by identifying which modulation signal <b>110</b>A-D produced the greatest relative change of capacitive effect in resultant signal <b>116</b>. Sensing channels <b>113</b>A-D experiencing such peak (maximum, minimum, or otherwise distinct) electrical effects could also be identified by comparing currently-observed, scaled electrical effects to baseline values (e.g. average values for the particular channel that are empirically determined, averaged over time, stored from a previous observation, and/or the like). Still other embodiments could identify the channel <b>113</b>A-D that produced peak electrical effects by comparing current electrical effects for each channel <b>113</b>A-D with current values observed in neighboring sensing channels. Alternatively, a weighted average of the electrical effects observed from some or all of the modulated electrodes <b>112</b>A-D can be computed, with this weighted average, or centroid, correlating to the position of object <b>121</b>. Many techniques for correlating electrical effects observed across sensing region <b>101</b> to a position of object <b>121</b> are known or may be subsequently developed, and any of these techniques may be used in various embodiments, according to the application.

0041By varying the digital codes <b>106</b> used to create modulation signals <b>110</b>A-D over time, various additional features can be implemented. To implement a simple dual-differential digital-to-analog conversion for received signal channels <b>113</b>, for example, the digital code <b>106</b> applied to one or more electrodes <b>112</b> is logically inverted (e.g. 1's complement) on a periodic, aperiodic, or other time basis to obtain complementary sensed signals <b>116</b>. The complementary codes <b>106</b> can be used to drive two separate ADC inputs (e.g. ADCs present in driver <b>115</b> and/or demodulator <b>117</b>) in opposite directions, thereby canceling out many types of variability or residual distortion in signal <b>116</b>. Steps <b>210</b> and <b>212</b> describe optional noise reconfiguration and image processing features, respectively, that may be enabled in various embodiments as additional benefits available from the use of spread spectrum techniques. These features are described in increasing detail below (in conjunction with <figref idref="DRAWINGS">FIGS. 3 and 4</figref>, respectively), and may not be present within all embodiments. Because the digital codes <b>106</b> are inherently simple to modify, store and subsequently process, any number of signal enhancement, noise reduction and/or other performance improvements to sensor <b>100</b> are enabled. Further, a relatively large number of digital codes are available due to the combinatorial power of digital sequences. Coding gain and orthogonality conventionally rely upon linearity and superposition of the particular codes used. Although non-linearity and dispersion limit the theoretical effectiveness of digital codes, these limitations can be more than offset by the increases in relative signal power (and thus SNR) that can result from simultaneously modulating more than one electrode <b>112</b>. Further, since it is possible that self-induced inter-channel noise dominates over other noise sources in many embodiments, a relatively stable dynamic range can be provided.

0042Referring now to <figref idref="DRAWINGS">FIGS. 3A-B</figref>, spread spectrum techniques allow for improved noise avoidance as compared to conventional single-frequency sampling techniques. As noted above, a sensing zone may correspond to a single electrode <b>112</b>, or a common modulation signal <b>110</b> may be provided to multiple electrodes <b>112</b> to create a larger sensing zone that effectively behaves as a single “electrode” for purposes of subsequent demodulation and computation. The modulated waveform <b>110</b>, being the function of a distinct digital code <b>106</b>, uniquely identifies the sensing zone to which it is applied, thereby allowing ready application of CDM and other conventional spread-spectrum techniques. <figref idref="DRAWINGS">FIG. 3A</figref> shows an exemplary spectral plot <b>300</b> that emphasizes the frequency domain differences between the spectrum <b>302</b> of carrier signal <b>111</b> and the spectrum <b>304</b> of modulated signal <b>110</b>. In contrast to a single-frequency carrier signal <b>302</b>, the multi-frequency spectrum <b>304</b> of modulated signal received on <b>114</b> is much wider. Because the spectrum <b>304</b> of the modulated signal distributes available power across a much wider sensitivity band, the effects of narrowband noise signals <b>306</b> at or near any particular frequency of interest are significantly reduced. That is, if a spurious noise signal <b>306</b> happened to occur near a single-frequency (or narrowband) carrier signal <b>302</b>, any electrical effects present within the sensing channel <b>113</b> could be overwhelmed by the noise. Moreover, adverse effects of wider-band noise <b>308</b> or interference from other modulated electrode channels <b>310</b> can be mitigated through spread-spectrum techniques, as shown in spectral plot <b>350</b> of received signal <b>116</b>. <figref idref="DRAWINGS">FIG. 3B</figref> shows an exemplary spectral plot <b>350</b> including a demodulated signal <b>352</b> (corresponding to coupling of a channel <b>113</b> and/or the presence of object <b>121</b> near the demodulated sensing region) is contained within a relatively narrow frequency band, whereas signals <b>354</b> received from other channels are spread across a wider band. Both wideband noise <b>308</b> and narrow band noise <b>306</b> are similarly spread across wider frequency bands <b>356</b> and <b>358</b> in the demodulated signal. By increasing the bandwidth of the applied modulated signal <b>110</b>, then, the signal-to-noise ratio in the demodulated signal <b>116</b> is improved dramatically. The demodulation in turn spreads the noise outside of the signal band, which then becomes quite narrow, thereby allowing the desired signal portion <b>352</b> to be readily extracted by a narrow band filter or the like. This concept can be further exploited by selecting digital codes <b>106</b> that avoid known sources of noise. That is, digital codes <b>106</b> of any bit length may be applied to carrier signal <b>111</b> to create spectral “gaps” at frequencies known to be susceptible to spurious noise. By applying conventional Fourier analysis (e.g. using a simple fast Fourier transform (FFT) or the like), digital codes can be selected to create modulation signals <b>110</b> having many desired spectral characteristics. Codes applied to any modulated electrode <b>112</b> can be modified during operation (e.g. step <b>210</b> in <figref idref="DRAWINGS">FIG. 2</figref>) and/or may be pre-selected to avoid expected or observed noise in resultant signals <b>116</b>. Alternatively, the particular codes <b>106</b> applied to one or more electrodes <b>112</b> may be randomly, pseudo-randomly, deterministically or otherwise modified during sensor operation, thereby statistically filtering any noise present within resultant signals <b>116</b> or demodulated signals <b>118</b> over time. Similarly, particular spatial frequencies or spatial positions can be emphasized (e.g. with code gain) or filtered out by the codes applied to different modulation electrodes. Code shifting during operation may provide other benefits (e.g. discrimination of or resilience to moisture) in addition to reducing the effects of noise or spurious effects of non-input objects (palm etc). In various equivalent embodiments, the frequency, phase, amplitude and/or waveform of carrier signal <b>111</b> may be adjusted in place of or in addition to modifying digital codes <b>106</b>.

0043With reference now to <figref idref="DRAWINGS">FIG. 4</figref>, spread spectrum techniques that simultaneously apply multiple coded modulation signals <b>110</b>A-D to various electrodes <b>112</b>A-D are able to identify multiple presences <b>408</b>, <b>410</b>, <b>412</b> of objects <b>121</b> located within sensing region <b>101</b>. Multiple objects may correspond to the presence of multiple fingers on a touchpad, for example, a palm resting on sensor <b>100</b> during use, simultaneous presence of a finger and a stylus, and/or any other combination of inputs. Electrical effects resulting from the various presences <b>408</b>, <b>410</b>, <b>412</b> can be conceptually projected along one or more axes <b>404</b>, <b>406</b> to identify the relative positions of the objects along that axis, as shown in <figref idref="DRAWINGS">FIG. 4</figref>. That is, peak value(s) of electrical effects can be correlated to relative positions of objects <b>121</b> with respect to sensing region <b>101</b>. In the example of <figref idref="DRAWINGS">FIG. 4</figref>, a finger <b>408</b> may be identified by increases in electrical effects projected along an “X” axis <b>404</b> and a “Y” axis <b>406</b>. By correlating the relative X and Y positions of peak electrical effects, the location of presence <b>408</b> can be correlated in two dimensions (or any other number of dimensions). Similarly, the example of <figref idref="DRAWINGS">FIG. 4A</figref> shows a larger area indicating a second presence <b>410</b> that results in projections of electrical effects in axes <b>404</b> and <b>406</b>. These multiple projections of electrical effects can be additionally correlated to identify images (e.g. “outlines”) of objects <b>121</b> present within region <b>101</b>. Taking this concept further, one or more images <b>408</b>, <b>410</b>, <b>412</b> may be subsequently processed as appropriate. Presence of multiple fingers within region <b>101</b> may be used to perform scrolling, mode selection or other tasks, for example. Similarly, if an image can be identified as resulting from a user's palm (or another undesired portion of the user's body), that image <b>410</b> can be subsequently rejected in future processing, such as reporting of positional information or other output signals.

0044In the exemplary embodiment shown in <figref idref="DRAWINGS">FIG. 4</figref>, the two axes <b>404</b>, <b>406</b> generally correspond to portions of modulated electrodes <b>112</b> or their associated channels shown arranged in two approximately orthogonal directions as in <figref idref="DRAWINGS">FIG. 1B</figref>. Alternate embodiments, however, may include any number of electrodes <b>112</b> arranged in any overlapping, non-overlapping, matrix or other arrangement. An example of a sensor <b>500</b> with overlapping electrodes <b>112</b>A-G arranged in two dimensions is shown in <figref idref="DRAWINGS">FIG. 5</figref>. In such embodiments, electrical effects on received channels can effectively be independently measured at each crossing of the electrodes in two directions (e.g. X and Y directions corresponding to axes of <b>404</b>, <b>406</b> in contour plot <b>400</b>), with the results correlated in controller <b>102</b> to provide a two-dimensional representation or image of object <b>121</b> rather than two one-dimensional “silhouettes” like <b>404</b> and <b>406</b>. In such cases, electrodes arranged in the first direction (e.g. electrodes <b>112</b>A-C) may be modulated at separate times from electrodes arranged in the second direction (e.g. electrodes <b>112</b>D-G), with one or more independent received signals <b>116</b> at any one time from either set of electrodes (e.g. electrodes <b>112</b>D&amp;F) being provided to demodulator <b>117</b> via a multiplexer <b>502</b>. <figref idref="DRAWINGS">FIG. 5</figref> shows the various electrodes <b>112</b>A-G coupled to both modulator <b>107</b> and demodulator <b>117</b> via a multiplexer <b>502</b>. The multiplexer may also connect one or more of the electrodes to receiving circuitry <b>115</b> before demodulation. In practice, each electrode may be connected in any manner to allow signals to be applied on one subset of electrodes <b>112</b> and received on another subset.

0045In various embodiments, two or more electrodes which serve to receive channels (e.g. analogous to channel <b>113</b> described above) may be provided with independent resultant signals <b>116</b>. Further, inactive or unused electrodes (e.g. <b>112</b>E&amp;G may be coupled to an electrical reference (e.g. ground) or driven with a modulated signal to improve spatial resolution on the active receive channels. This reference is commonly referenced as a shield or guard signal, which may be applied via multiplexing logic <b>502</b> or the like.

0046Digital coding and other spread-spectrum techniques may be equivalently applied in sensors that operate in any number of different manners. <figref idref="DRAWINGS">FIG. 6A</figref>, for example, shows an exemplary sensor <b>600</b> that includes any number of modulated electrodes <b>112</b>A-B arranged in any single or multi-dimensional fashion that are coupled to a capacitive filter circuit <b>604</b> (which may include an integrating capacitor <b>610</b>) which linearly transforms the charge transferred by the modulated electrodes. A microcontroller <b>102</b>/<b>104</b> or the like suitably generates distinct digital codes <b>106</b> that modulate the transmitter electrodes <b>112</b>A-B which are capacitively coupled to the one or more receiver electrodes <b>114</b> as described above. In this case, however, the digital codes <b>106</b> are not necessarily intended to encode the voltage provided to each electrode <b>112</b>A-B, but rather to control the timing of charge that is transferred to receiver electrode <b>114</b>. By controlling the timing of each electrode's charging and discharging and then observing the amount of charge collected at integrating capacitor <b>610</b> from receiver electrode <b>114</b>, the amount of charge provided by each electrode <b>112</b>A-B can be determined from the demodulated signal <b>118</b>. The charging of each electrode <b>112</b>A-B can be controlled by selecting digital codes <b>106</b> such that voltage is applied to each electrode only when charge should be transferred to the receiving electrode <b>114</b>, and otherwise allowing it to float. By selectively providing charge from individual and/or groups of electrodes <b>112</b>A-B to capacitor <b>610</b>, the amount of coupling from each electrode <b>112</b>A-B (which is affected by the proximity of an object <b>121</b>) can be determined.

0047<figref idref="DRAWINGS">FIG. 6B</figref> presents an alternate embodiment of an exemplary sensor that has unified sensing and driving on each electrode <b>112</b> that is filtered or demodulated by one or more capacitors <b>610</b>. The codes <b>106</b> modulate drive circuitry <b>109</b>, which may be implemented as a current source connected to the electrodes <b>112</b>. The response of the electrode to the drive circuitry is affected by the coupling of an object <b>121</b> near the electrode, and the resultant signals (e.g. the voltage resulting from the coupling) are filtered and/or demodulated by the circuit <b>604</b> and capacitor <b>610</b>. The filtered signals may be further demodulated to determine position attributes of the object. Further, more than one electrode could be simultaneously driven with substantially orthogonal codes and after demodulation a stable coupling of one electrode <b>112</b>A to another electrode <b>112</b>B would substantially cancel out. These and many other position sensing methods benefit from digital coding and spread spectrum techniques.

0048With reference now to <figref idref="DRAWINGS">FIG. 7</figref>, various sensors <b>700</b> formed in accordance with the coding techniques described herein may be formed on a single circuit board or other substrate <b>702</b>. In such embodiments, electrodes <b>112</b>A-G forming sensing region <b>101</b> may be disposed on one side of the substrate, with the processing components (e.g. controller <b>102</b> and the like) formed on the opposite side. Because various sensors (e.g. sensors <b>100</b> and <b>500</b> shown in <figref idref="DRAWINGS">FIGS. 1 and 5</figref>) do not require physical movement of sensing and receiving electrodes <b>112</b>, <b>114</b> with respect to each other, electrodes <b>112</b>, <b>114</b> in such sensors may be rigidly fixed on substrate <b>702</b> in any manner. Substrate <b>702</b> can be made of a flexible material to allow for folding or bending. Further, a protective surface <b>704</b> may be deposited or otherwise placed over the electrodes to provide consistent dielectric isolation and to protect against moisture, dust and other environmental effects. Surface <b>704</b> may also provide tactile feedback to the user as appropriate. <figref idref="DRAWINGS">FIG. 8</figref> shows an exemplary sensor <b>800</b> is formed on a flexible substrate <b>802</b> as appropriate. <figref idref="DRAWINGS">FIG. 8</figref> also shows that the various processing components may be found on the same side of substrate <b>802</b> as the modulated and sensing electrodes, and that the substrate <b>802</b> may also provide tactile feedback for region <b>101</b>. It should be appreciated that the various concepts, structures, components and techniques described herein may be inter-combined and/or modified as appropriate to create a wide variety of alternate embodiments.

0049Accordingly, there are provided numerous systems, devices and processes for detecting a position-based attribute of a finger, stylus or other object in a position sensing device such as a touchpad. While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. The various steps of the techniques described herein, for example, may be practiced in any temporal order, and are not limited to the order presented and/or claimed herein. It should also be appreciated that the exemplary embodiments described herein are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Various changes can therefore be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.